|MadSci Network: Medicine|
Good question and good insight into advertising. Don't believe everything you hear. There are two issues here. First, both the coating of a pill or the filler material that it is mixed with have an effect on how fast the pill dissolves and how fast the drug becomes soluble in the fluids in the small intestine. The drug company can manipulate these to make a pill that dissolves very quickly or very slowly. They can make multiple kinds of tiny, tiny pills for the same medicine, some that dissolve very slowly and some that dissolve very quickly. These can then be mixed and put into a capsule (among other possibilities). The result is that some of the medicine dissolves quickly and some slowly so that you have a longer time that the medicine is being circulated in your body. For example, the drug Sudafed (aka pseudoephedrine) can be bought in the drug store in two different forms. It's used to dry up runny noses (a decongestant). In one form, it contains 30 milligrams of drug that dissolves fast and is available to the body fairly quickly. The other form has 120 milligrams but if made so that it dissolves slowly so that the higher dose is released over about 10- 12 hours. This is supposed to provide long-term relief for your nose. If you used only the smaller pill, you'd have to take one every 3-4 hours. With the slowly dissolving or "time-release" form of Sudafed, you take one pill every 12 hours. Second, and more specifically to the advertising, most of the ads that say this or that medicine quickly dissolves and therefore gives your relief faster are really stretching the truth quite a bit. I won't call the statement completely wrong but it is very deliberately misleading. The simple fact is that most drugs dissolve pretty quickly in the stomach and small intestine, usually within 15 minutes. Making sure they dissolve in 5 min really doesn't change things very much. The limiting factor is not how fast the drug dissolves but how fast the drug can be absorbed across the wall of the small intestine into the blood. The speed at which a drug dissolves has absolutely no effect on how fast the drug can be absorbed by the intestine. Perhaps, because a drug dissolves completely in 5 min instead of 15 min there would be more drug available to be absorbed in those first few minutes, but there's a limit on how fast the intestine can absorb the drug, so it doesn't make much of a practical difference. At best, your headache might start going away in 10 minutes instead of 15 minutes. As an additional point, drugs are NOT absorbed in the stomach. They are absorbed virtually exclusively in the small intestine. In some cases, you may not want the drug to dissolve quickly. The stomach is very acid and could cause the drug to break down, and in a very few cases even injure the stomach. The small intestine is much less acid and the drug won't break down there. The absorption occurs in the small intestine simply because the total surface area of the small intestine is very, very large compared to the surface area of the stomach. About 10,000 times greater. The speed at which a drug is absorbed is directly related to surface area, so most of the absorption occurs in the small intestine.
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